- 期刊
蒸汽管膨脹接頭表面裂紋原因分析
Investigation of Crack Formation on the Expansion Joint Surface of the Steam Tube
摘要
In the process of expansion joint replacement and welds examination of steam tubes, the obvious cracks were observed on the surface in the vicinities of the welds near the joined tube, however, not in the welds and matrix. In order to realize why the cracks reveal, the failed materials were thus analyzed. Two kinds of metallurgical structures, including ferrite and pearlite, are found from the cross section observation for above two specimens. However, they are quite different in the microstructure. For the expansion joint, two structures present alternately in the specific orientation and parallel with longitude direction of the tube showing band rolled structure. The equi-axial crystal with lager grain size is demonstrated on the jointed tube instead. Otherwise, the severe decarburization is depicted in the outer and inner side of the joined tube. From the XRD analysis results, FeO, only formed in the high temperature (＞ 570℃), is found on the corrosion product from tube inside. It expresses that the joined tube had ever gone through high temperature treatment. However, the operation temperature of the tube is in the range from 180 to 190℃. Under the temperature, the wide oxide layer existed in the vicinity of the cracks should not be found. Therefore, it suggested that the cracks on the surface of the joined tube had existed before operation which is related to the combination of the unsuitable high temperature treatment and applied stress.
並列摘要
In the process of expansion joint replacement and welds examination of steam tubes, the obvious cracks were observed on the surface in the vicinities of the welds near the joined tube, however, not in the welds and matrix. In order to realize why the cracks reveal, the failed materials were thus analyzed. Two kinds of metallurgical structures, including ferrite and pearlite, are found from the cross section observation for above two specimens. However, they are quite different in the microstructure. For the expansion joint, two structures present alternately in the specific orientation and parallel with longitude direction of the tube showing band rolled structure. The equi-axial crystal with lager grain size is demonstrated on the jointed tube instead. Otherwise, the severe decarburization is depicted in the outer and inner side of the joined tube. From the XRD analysis results, FeO, only formed in the high temperature (＞ 570℃), is found on the corrosion product from tube inside. It expresses that the joined tube had ever gone through high temperature treatment. However, the operation temperature of the tube is in the range from 180 to 190℃. Under the temperature, the wide oxide layer existed in the vicinity of the cracks should not be found. Therefore, it suggested that the cracks on the surface of the joined tube had existed before operation which is related to the combination of the unsuitable high temperature treatment and applied stress.